The present invention relates to an apparatus for carrying out dry etching, and more particularly to a dry etching apparatus used for forming patterns of semiconductor integrated circuits.
In the fabrication of semiconductor devices, particularly LSI circuits, a dry etching process is necessarily required. Such a dry etching process is roughly classified into a method based on physical reaction and a method based on chemical reaction. A typical method of the former is a sputter etching method and a typical method of the latter is a CDE (Chemical Dry Etching) method.
TABLE 1 __________________________________________________________________________ Etching Reaction .rarw. Physical reaction Chemical reaction .fwdarw. Etching method Sputter RIBE, RIE, Plasma CDE etching, etching, Etching characteristic .rarw. Good anisotropy Poor anisotropy .fwdarw. Poor selectivity Good selectivity Damage .rarw. Large Small .fwdarw. Sample SiO.sub.2, Si, Doped Si, Al __________________________________________________________________________
As indicated in Table 1, etching methods of intermediate characteristics therebetween are RIBE (Reactive Ion Beam Etching) method, RIE (Reactive Ion Etching) method, plasma etching method, etc. A study is made to compare the method based on the physical reaction with the method based on the chemical reaction in connection with the etching characteristic. Since the former method is an etching due to irradiation of ion beam etc., a reaction proceeds along an ion advancing direction, resulting in good anisotropy, but sputtering yields (the numbers of target atoms removed per one incident particle) between materials are not different from each other to much extent, resulting in poor selectivity therebetween. In contrast, since the latter method is an etching utilizing chemical reaction due to activated species, the activated species are isotropically diffused. As a result, anisotropy becomes poor, but the reaction is greatly varied depending upon kinds of activated species and samples, resulting in good selectivity. Further, in regard to damages to the sample, even when either method is employed, the surface of the sample is damaged by the exposure to ion beam or plasma. However, the degree of the damage by the method based on physical reaction is larger than that by the method based on chemical reaction. The method based on physical reaction is mainly used for etching the sample, e.g., SiO.sub.2 or Si, etc. and the method based on chemical reaction is mainly used for etching the sample, e.g., doped Si or Al, etc.
The etching employed in the manufacturing processes for LSI has the following three requirements. First is that anisotropy is excellent. Second is that selection ratio between materials is large. Third is small damage. The first requirement is necessarily required for high precision dimension control. In the recent LSI, pattern formation of the circuit dimension of approximately 1 .mu.m is required. To effect an etching faithful to a resist pattern as a mask, etching having excellent anisotropy is required. The second requirement on the selectivity is necessarily required for etching integrated semiconductor devices. A gate oxide film increasingly becomes thin and the employment of a shallow junction as a junction layer of a semiconductor is now generalized. For instance, in case where there arises a need such that a gate oxide film is left to remove other layers by etching, an employment of an etching process having poor selectivity results in the fact that even the gate oxide film is removed. As a result, there is a possibility that there occurs an opening in the gate oxide film. Thus, according as the integration is developed, an etching process having higher selectivity is required. In addition, in regard to the third requirement on the damage, an etching method having less damage is desired for the same reason stated above.
However, the above-mentioned both methods have advantages and disadvantages, viz., the etching process based on physical reaction has good anisotropy but poor selectivity, whereas the etching process based on chemical reaction has good selectivity but poor anisotropy. On the other hand, with other processes, e.g., RIBE, RIE and plasma etching, etc. which lie in the middle of the above-mentioned two methods, it can be said that they stand on an appreciable point of compromise but fail to provide excellent anisotropy or excellent selectivity. Further, these methods cannot control an energy or density of ions independent of other parameters, e.g., density of activated species, etc., failing to provide optimum etching conditions. For instance, the reduction of an energy of ions solely depends upon an indirect method, e.g., a method of lowering a high frequency power used for excitation of activated species, a method of raising a pressure within a chamber or the like. Thus, this results in changes in other etching conditions.
As stated above, the drawback with the above-mentioned conventional dry etching apparatus is that it is unable to set optimum etching conditions depending upon the quality of the sample to be etched or an etching pattern.